I have been flying airplanes for about five years, I hated expo's until I started off with the t-rex about eight months ago. It helped me with the minor mistakes I would make when learning to piroutte when hovering, and everyting else when learning the basics. I'm past the rex for now, went to the TT30 for about a month and am now flying a 90 class (and a tragic crash on a first flight, equipment faluire). I have programmed expo's in every new heli that I fly, and after a few test flight's and dialing in the feel that is natural to me, I end up with no expo's. Is this normal? Everyone that I fly with has a considerable cross range of experience and they all say to use some form of exponetial programming. What does everyone else use?

Ryan.

Aside from acquiring smoothness near the middle of the stick throws, the choice of whether or not to use expo also has to do with how far a particular servo rotates to do its work.

If a servo has a long arm and doesn't move more than 40-50 degrees to do it's work, then less expo (if any) on that channel would be used to make up for the geometry change of the linkage as the servo rotates. If a servo has to rotate 70-80 degrees or more to accomplish full travel of the linkage, then 20-30% expo will go a long ways towards matching the stick movement to the control surface movement as the geometry changes.

On my R50 the collective servo is the one that moves the most to do it's work. I use a pitch curve of 100-70-50-30-0, which is like having a bit of expo on collective, mostly for the purpose of compensating for the geometry change at the ends of the throws. My aileron and elev servos both rotate about 60 degrees. I use 20% on those two to smooth out the middle of the cyclic stick throws. I tested the difference and it's really only slight, but helpful for the slow smooth stuff.

I like zero expo on rudder. I wanna be able to move the tail quickly no matter what.

Expo . . . hmmmm.

If you look at the typical linkage arrangement, you see that the servo output is rotary and linear response in the arc. With full servo travel being +/- 45º, the output push rod will move only 70% (cos 45º) as much at the ends as it does at center. So, to get a reasonably linear pushrod movement over the full range, sounds like 30% expo is indicated.

I use 15% expo on my cyclics - just to smooth things out in the hover (normal+inverted). I use 9deg of cyclic deflection and so expo helps out in hovering.

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Don't get into any mechanical linearity via software exponential debate, that's just a layman's misconception that gets argued to no end.

I don't know if it's possible to counter the sensitivity curve of one rotational deflection with another rotational deflection or not though. I've never really put thought into that. Seems to me, more rotational deflections can only either maintain the sensitivity curve, or sharpen it, or just plain warp it if it's not centered throughout. I can't picture countering it.

Thankfully we have software exponential that can change the sensitivity curve to our liking however the mechanics shape it.(well not if it's warped off center)

Expo can also be used to help prevent input intereaction between the two controls assigned to each stick. (accidental rudder input when controlling the collective, etc)

What you say is true, BUT the end result is moving the blade grip around a circle,(adding and losing pitch change, per degree of servo arm,blade grip movement) so are'nt most of these effects canceled out?
Just a thought

No, it doesnt cancel out, it translates from a rotational output to a linear output to a rotational input.

You have still lost linearity from the servo, and you are not getting any linearity back when the blade grip turns.

Just like the servo, the push rod pushing the blade grip would still need to be moved more and more to match the transmitter stick motion

You see the problem is the relationship between the transmitter stick and the servo/output arm and the use of bellcranks in helis.

If the servo was directly mounted to the bladegrip then there would be no problem there wouldnt be any bellcranks or pushrods, but that would be a really stupid design idea.

In the end, the servo arm is about half the lenth of the moment arm at the main blade . . . so . . . yes . . . expo does tend to linearize the motion.

I used to use Expo when I had my Xcell 46. I started flying my R50 with Expo, binned it off and my R90 is as is, In fact the 90 has the V Blades paddles and about 7 degrees cyclic pitch and still could do with rolling FASTER!

I'm glad you came back and cleared that up Wolfgang, I thought you might have opened a can of worms with that previous post. I know you were really responding to the post after that though.

It should be added that expo will only have a linearizing effect on cyclic and rudder, but if you are using a HH gyro it will not have this effect since a HH gyro will just drive the servo to where ever it has to go to hold the heading (within the throw limits)

Expo on the rudder with HH just has the effect of softening the centre of it, nothing else.